1. Field of the Invention
The present invention relates to a wireless communication system, and more particularly, to a method and apparatus for transmitting an uplink Reference Signal (RS) to a Base Station (BS) at a User Equipment (UE).
2. Discussion of the Related Art
A 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) communication system will be described below as an exemplary mobile communication system to which the present invention is applicable.
FIG. 1 illustrates the configuration of an Evolved Universal Mobile Telecommunications System (E-UMTS) network as an example of a mobile communication system. The E-UMTS system is an evolution of the legacy UMTS system, under standardization in 3GPP. E-UMTS is also called LTE. For details of the technical specifications of UMTS and E-UMTS, Release 7 and Release 8 of “3rd Generation Partnership Project; Technical Specification Group Radio Access Network” can be referred to, respectively.
Referring to FIG. 1, the E-UMTS system includes a UE, evolved Node Bs (eNode Bs or eNBs), and an Access Gateway (AG) located at an end of an E-UTRAN and connected to an external network. An eNode B can simultaneously transmit a plurality of data streams for multicast service and/or unicast service.
An eNode B covers one or more cells. Each cell is set to one of the bandwidths of 1.25, 2.5, 5, 10, 15 and 20 MHz and provides downlink or uplink transmission service to a plurality of UEs in its bandwidth. Different bandwidths may be allocated to different cells. The eNode B controls data transmission and reception to and from the plurality of UEs. Regarding downlink data, the eNode B notifies a UE of an allocated time/frequency area, a coding scheme, a data size, and Hybrid Automatic Repeat reQuest (HARQ) information. Regarding uplink data, the eNode B transmits information about an allocated time/frequency area, a coding scheme, a data size, and HARQ information to a UE that is to transmit the uplink data to the eNode B. An interface may be established between eNode Bs, for transmitting user traffic or control traffic. A Core Network (CN) may include an AG, a network node for performing user registration of UEs, etc. The AG manages the mobility of UEs on a Tracking Area (TA) basis, a TA including a plurality of cells.
The developmental stage of wireless communication technology has reached LTE based on Wideband Code Division Multiple Access (WCDMA). Nonetheless, demands and expectation of users and service providers for advanced wireless communication services are still rising. Considering that the development of other competing wireless access technologies is in progress, a new advanced technology is needed to achieve future competitiveness. In addition, efforts should be expended toward reduction of cost per bit, increased service availability, flexible use of frequency bands, a simplified structure and open interface, and appropriate power consumption of UEs.
The 3GPP has recently been working on standardization of a successor to LTE. The successor to LTE will be referred to as “LTE-Advanced” or “LTE-A” herein. A major difference between the LTE system and the LTE-A system lies in that the latter supports uplink transmission in a multi-antenna technique.